Nginx truncate my data.

I need to output large data, but nginx will truncate it.
I test it with nginx 0.7.67
when the data is more than 40K, I could only get part of it, using curl
apache is the backend of nginx, so I also test apache using curl
directly, and everything is OK.
So I think it's nginx who eat my data.
I have closed gzip, and nothing changed.
Do you have any idea?
Posted at Nginx Forum: http://forum.nginx.org/read.php?2,155180,155180#msg-155180